This invention relates to capacitor banks in general, and more particularly, to an improved protective circuit arrangement for a high-voltage capacitor bank.
Protective circuit arrangements in which a high voltage capacitor bank having at least two equal parallel branches connected to one phase of a power supply system, each branch containing several individual capacitors in series with each other and with a current measuring device and having a differential protection device followed by monitoring means coupled to the current measuring devices are known. In general, these systems rely on the fact that if a defect occurs in the capacitor bank an asymmetry between the two branches will occur. The differential protection device responds to the asymmetry to give an output indication so that the necessary action can then be taken. However, in a bank of high voltage capacitors, asymmetries can also occur during normal operation of the system. For example, such can occur because of individual capacitors being subjected to different ambient conditions. The prior art circuit arrangements are unable to distinguish between asymmetries caused by a failure and asymmetries simply resulting from normal operation. As a result, they respond to both and provide, in many cases, a false alarm.
In view of this difficulty with prior art systems, the need for an improved system which does have the capability of distinguishing between asymmetries related to the operation of the system and those caused by a failure or defect in one of the individual capacitors is evident.